Tuesday, August 28, 2012

Custom Crosman Breech--Part 7 Finishing the Loading Bolt

Just picking up where I left off.

Spotted the bolt.

Drilled a 3/16" diameter blind hole.

Used a flat bit to finish the bottom.

Spotted again on the end.


Tapped #6-32.

Added a setscrew that will retain the bolt handle.

A piece of 3/16" O-1 drill rod was used as the handle.   Not shown:  Hand filed a small flat for the setscrew to bear against.

Now for the plunger.  Faced a piece of 0.500" free-machining steel.

Through drilled with a 3/16" to fit over the handle.

Followed by partially drilling with a 5/16"--leaving a stepped hole.

Another piece of free machining steel was turned down to 5/16" OD on one end.

Drilled into the piece with a 4.2mm bit.

Followed by a M5 x 0.8mm tap.

The piece was parted off and the cut end faced/finished.

Removed the 3/16" bolt handle and found an M5 x 0.8 thread cutting die.  Thread cutting dies are typically round, split dies that have an adjustment for thread cutting depth.  Not to be confused with the hex shaped dies from hardware stores that are normally only suitable for chasing (cleaning up) damaged pre-existing threads.

With the die in a holder, the piece was chucked and the Taig lathe used for alignment.

Here's the loading bolt/handle components.

The M5 threads were Loctited and assembled.  With 680 Loctite, a 5mm thread is never going to come apart.

Spring goes over the handle and bears against the cap.

Sleeve fits over the handle with the spring inside.  The sleeve will need some knurling or grooves (or maybe a complete remake) to add some finger traction.  That can happen later.

Handle fits into the bolt and the setscrew locks it in place.

Test fit.

Forward, fire position.  The spring loaded plunger locks into the forward recess in the cocking slot.

Here's where the grasping grooves would come in handy.   The sleeve is pulled outward against the spring to unlock the bolt.

Then slid back to cock the hammer.  Returning it forward loads the next pellet from the Marauder magazine.

It can also be locked back in the rear position to change mags with no worry of the thin bolt probe extending into the magazine slot and being damaged.

Not covered here:  The taller than factory breech required a longer than factory cocking pin in the hammer.  Just used a piece of 1/8" drill rod and cut it to length.  If I end up needing something more elaborate, I'll cover it.

The transfer port also needed rework since the taller breech meant the stock component was far too short.  This is a piece of 0.250" brass.

Cleaned up the ends and through drilled with, I forget exactly, uh, probably something around a 5/32" bit.

With a depth gauge and some
elementary math, I figured out the "relative" length of the brass tube.

"Relative" because I added an o-ring to each end and there's some compression to factor in.  Since it worked perfectly on the first test assembly with no gas leak, there's strong evidence that this isn't a critical tolerance component.

So, yeah, it actually works.  Still several immediate things need attention--like adding sights or dovetails, fitting the shroud, making it look less "blocky", maybe an actual finish...

Check back in a couple days.